Growing up with his two brothers in Mount Vernon, Ohio, near Columbus, gardening was a chance for George Pealer to spend time with his dad.

“It wasn’t a huge garden, but that wasn’t the point,” George says. “He spent a few hours a week out there and he let me tag along.” When he got to high school, the Pealers moved to Bexley — a larger Columbus suburb — where George worked at Connell’s Flowers. At the time, it was one of the largest florists in Ohio.

“It was a bit of shock, but it was probably the best thing for me, moving away from a small town,” he says. “Connell’s had a greenhouse and a plant retail business, so I was able to work in the greenhouses and help out in the flower shop and receive flower shipments. It really got me interested in growing flowers.”

In his career, George has served on the board of directors of the Ohio Nursery and Landscape Association and as the president of the Perennial Plant Association while Millcreek became one of the first nurseries in the Ohio Valley region to sell herbs on a wholesale basis. Today, he is still at the business every day, trying to help it grow and help every employee succeed.

“He’s at the forefront,” says Fred Higginbotham, Millcreek’s growing operations manager. “He will just come up and say, ‘Tell me where I can pitch in; tell me where I can help out.’ No job is too big or too small for George. People see that commitment he has.”

The defining relationship

In George’s last quarter at Ohio State, he met his future wife, Lynda, in a greenhouse management course. They started dating soon after.

“She was a very strong woman,” George says. “She went to Purdue University and had a degree in microbiology, and when she graduated, she worked at a medical center in Indianapolis doing cancer research. She realized after a year or two that she didn’t want to spend her life in a lab. She had been married, had children and got divorced.” George says Lynda came to Columbus with an interest in horticulture and knew Ohio State was a good opportunity for her to begin doing the kind of work she wanted. Ultimately, she got a horticulture degree from Ohio State.

The two married in 1977 and founded Millcreek Gardens a year later in February. Before starting the business, the two traveled together, visiting operations such as White Flower Farm, a nursery in Connecticut, and Gilbertie’s Organics, an herb farm in Connecticut, and thought the operations set a blueprint for them to found a business together.

At the beginning, George returned to work at Connell’s for three more years as the business got going. At Millcreek, they combined two passions — George’s for perennials and Lynda’s for herbs — into one combined vision. They settled down in Ostrander, located just outside of Columbus, and for a long time, Lynda grew the herbs day in and day out. When she took a step back from growing, she still helped behind the scenes.

“The thing that always impressed me about Lynda was that she loved herbs, and loved to cook with them, but couldn’t find them anywhere,” George says. “But we saw them [on our trip] and she thought it would be great to do them here. She was really a pioneer in our area for growing herbs in pots like you see now. It’s such an integral part of our company now. People know us for our perennials and our herbs.”

Lynda died on Christmas Eve in 2018, leaving behind George, six children and 12 grandchildren. She made an impact on everyone she met.

“She had extremely high standards,” says Nathan Pealer, George and Lynda’s son, who works in real estate. “She pushed everybody to be better. And since she had such high standards, everybody tried their best around her, be it her family or someone at work. She held herself to those same high standards, too.”

“She was only here for a couple of years when I started here,” says Higginbotham, “But I’d never seen a man have as much love for his wife as George had for her.”.

Helping others grow

Higginbotham first visited the company in the early 2000s during an open house, recalling thathe was “blown away” by the facility even back then. After interning at Millcreek one summer and graduating from Ohio State the next spring, he joined the company in 2005. He started out as an assistant grower, became a head grower, and then was finally promoted to his current role as growing operations manager about five years ago.

From the time he first visited Millcreek, Higginbotham saw that George went out of his way to help him however he could.

“Throughout the years, the thing I can stay about George is that he’s the nicest guy ever,” Higginbotham says. “He treats everybody from seasonal employees to somebody who’s been here for 25 years exactly the same, always with a smile on his face. It’s one thing that sets George apart.” Higginbotham says that it is not uncommon for George to hop in and help with shipping, putting stickers on pots or bringing out cold Gatorades for the workers in the greenhouse.

“It’s about the people,” he says. “We have people that have been here 20, 25 years plus. Like any good organization, the good starts at the top and works its way down. And while George is very involved, he lets a lot of us on the management team have the freedom to do what we do and do our jobs. I’ve always appreciated that there’s a lot of trust involved here.”

Another employee George helped empower is Megan Armstrong, the company’s assistant general manager and business office manager. For the first part of her career, Armstrong was a grower working with gallon-size perennials and, in 2004, was named the Perennial Plant Association’s Young Professional of the Year. In 2012, she was promoted to assistant general manager, taking on responsibilities outside of growing like budgeting, staffing and overall company management.

According to Armstrong, it was a change she wanted, and one that George encouraged her to seek out.

“One of the biggest things is the trust George places in people,” she says. “He may challenge you for an idea, like developing a new product line for the slow season, but he’s not going to pigeonhole you. He wants your input, wants your ideas and is willing to go for it.”

Both Armstrong and Higginbotham both say that, amid the coronavirus pandemic, George has been essential in keeping the company connected while also prioritizing employee safety while working and trying to keep business as normal as possible.

For George, at the end of the day, empowering employees is part of the ethos he and Lynda set out to create when they founded Millcreek. To him, along with quality and profitability, values like integrity, leadership and teamwork are part of Millcreek’s DNA. Ultimately, a significant part of his legacy is helping people find their passion, just as his dad, his Ohio State professors, and his first employer did for him.

“Our mission statement is ‘growing high quality plants, people and relationships,’” George says. “For us, that says it all.”

For growers considering supplemental lighting, cost is a major factor to consider, said Dr. Marc van Iersel, a professor at the University of Georgia and co-founder of Candidus, a supplemental lighting control company.

Recently, he hosted a webinar with GLASE titled, ‘Lighting approaches to maximize profits.’ It is available in full here.

Determining cost

GLASE, in coordination with the Cornell College of Agriculture and science, created a lighting cost calculator for supplemental lighting need.

“What this calculator does is show how much supplemental light you need over the course of a year in order to make sure your crop receives 17 mols of light. Seventeen mols is a common amount for growing lettuce,” van Iersel said in the webinar.

Using lettuce production as an example, the calculator outlines two different scenarios for growers depending on if they are growing in a poly greenhouse with an estimated 62% light transmittance rate or in a glass greenhouse with an estimated 70% transmittance rate. While the color-coded maps — which detail how much supplemental light is needed each year for a specific area — are similar, there are differences in certain parts of the U.S., including Texas, Oklahoma, Georgia and South Carolina.

He added that growers in glass greenhouses need less supplemental light because they receive more natural sunlight due to the higher transmittance rate.

“Once you know how much supplemental light you need to provide and you know how efficient your lighting system is, plus the cost of electricity, it becomes really easy to calculate cost,” van Iersel said.

The amount of mols needed does vary by crop. Tomatoes, for instance, have a DLI target of 25 mols. As a result, the map looks different even with the same transmittance rate.

“Tomatoes require more light,” van Iersel said. “It’s a lot more light as compared to lettuce.”

In the coming months, van Iersel said an online calculator for growers to determine costs for their specific zip code, crop and lighting type will become available. Neil Mattson, a researcher at Cornell, has also released a tool to help growers determine their lamp seeds. It is available at hortlamp.com

The importance of the Daily Light Integral

According to van Iersel, the DLI has been used in greenhouse production for roughly 30 years and is primarily used for lighting recommendations.

“I think the daily light integral and using recommendations based on it is really useful,” he said. “But one thing we’ve been able to show is not all daily light integrals are calculated equally. How you provide that light over the course of the day also matters.”

Van Iersel said this is because of natural light variation. The amount of light and its variations depending largely on a geographic region.

In the webinar, van Iersel compared Elmira, New York, and Phoenix, Arizona. Elmira’s varied greatly due to the changing weather based on the season. In the winter towards the end of the year, for instance, much less light (as measured in mols) was created naturally. So, a grower in Elmira would need more supplemental light. By comparison, Phoenix still saw a dip in natural light towards the end of the year. However, because Phoenix does not have the same winter climate as Elmira, it doesn’t drop off nearly as much. It also varied much less day-to-day over the course of a year.

“In Phoenix, because it is typically sunny all year, there is just must less variation,” he said. “But you still have less light in the winter.”

For growers, that means understanding how the daily light integral is applied in their specific region. In the webinar, van Iersel showed a rudbeckia study where the same DLI – in this case, 12 mols – was applied over four different time frames (12 hours, 15 hours, 18 hours and 21 hours) vs. a control group with no supplemental light. The results showed, generally speaking, that plant growth improved as the photoperiod expanded.

“What we found is that as we go from a 12-hour photo period to a 21-hour photo period, we got a 33% increase in above-ground growth,” he said. “We also got a 22% increase in root dry weight.”

As for profit, van Iersel said the key is to use this data and find the right balance of spending on lighting in relation to pricing.

Take-home message

One other note van Iersel offered is that current research suggests that stability is best when applying light. That means it is better to apply the same amount of light vs. a variation during a growing cycle. An overlooked tool in helping that is using different greenhouse control systems to keep light levels consistent.

He also said it is essential to work with a lighting company that can help estimate various costs and develop a specific plan.

“If you’re working with a company that doesn’t have those resources available, you’re probably working with a lighting company that doesn’t know what they are doing,” van Iersel said.

Reduced plant growth in fresh wood-based substrates has been attributed to several factors including fertility, irrigation, and most commonly toxins (phytotoxicity).

Evidence of this condition has been published and observed for decades when growing in substrates that contain certain types and percentage of fresh (non-composted) and untreated wood materials.

The wood chemicals (secondary metabolites) responsible for inhibiting seed germination and stunting herbaceous plant root and shoot growth, are vital to the health and defense of trees while standing, but they need to be removed or rendered harmless before being used as a substrate to grow plants. These wood chemicals, known as extractives, are a group of compounds (either volatile or soluble) that vary in type and concentration depending on tree species and origin (region of growth).

Extractives are found in higher concentrations in older trees (thicker bark and more heartwood) than in younger trees (thinner bark) and the amounts in any given tree can fluctuate with different seasons of the year. Additionally, the amount of potentially harmful extractives is higher in tree bark and heartwood compared to softwood.

With these as well as other factors being known, tree species, tree age, harvest season, and the presence of bark should be considered when selecting or acquiring wood feedstocks to produce substrate materials.

Strategies for removal

Wood extractives, which research has shown to be less harmful to woody plants (rooted nursery liners for example) compared to herbaceous plants (seeds, plugs, transplants), can be successfully removed or mitigated by one of several strategies.

Better yet, once toxins are removed, growing quality plants in 100% wood substrates is possible as seen in Fig. 1.

Note that there are many variables to each of the following procedures that cannot be fully addressed in this article, but more information will be released in the future as research continues.

Wood processing method

After feedstock selection, the type and method of processing that wood chips undergo is a critical step in removing harmful extractives.

There is roughly a half dozen commercial machine types used (globally) to produce wood substrate products but three are most common: hammer mills, single or twin-screw extruders, and twin disc refiners. Each of these technologies function differently to reduce/separate wood chips into fibers or smaller wood chip particles.

Each of the methods also differ in their initial set-up cost, operating costs, annual maintenance costs, the range of size and moisture content of wood chips they are able to process, and ability to produce different particle sizes and shapes.

The primary features of the different machines that are responsible for the reduction or elimination of harmful wood extractives are heat generation, pressure, friction, and/or dry or wet processing. Heat and pressure (together or separate) are known to drive off (volatilize) wood extractives into the air. Exposure to a water or chemical solution bath for some period of residency time has also been shown to effectively solubilize certain extractives from wood chips.

Either by one, or both of these factors, wood chips can be refined to smaller particle sizes suitable for substrates and at the same time have their inherent chemicals removed in the process. Let’s take a look how the three machine types differ.

Hammer mills, the cheapest and most common of the methods, are used universally for processing many types of organic materials. Hammer mills operate by pulverizing particles with swinging hammers (or knives) until the material is reduced in size enough to pass through a perforated screen (Fig. 2A).

Wood chips typically need to be dry (under 40% moisture content) when processed in a hammer mill to prevent clogging. During the operation of the mill there is some heat generated, but the amount and extent is mostly proven negligible in significantly volatilizing wood chemicals. There is, however, some minimal chemical volatilization occurring as a direct result of the reduced (smaller) particle sizes being exposed to the air and dried during processing.

The heat that is generated in a mill depends on the moisture of the wood chips being processed, rpms and operational speed of the machine, and time of year of processing. Twin-screw extruders (Fig. 2B) have opposing screws that apply mechanical energy to wood chips which crushes, shears, and squeezes them to separate the wood fibers. During the process the pressure can rise to 500 kilopascals (~75 pounds per square inch – PSI) and the temperature can reach 210 – 230 °F (100 – 110 °C). After passing through the screws, a sudden “relaxation” of friction and pressure creates a steam explosion which results in further tearing of the wood fibers.

The friction heat and pressure effectively volatilize many wood extractives, thus mitigating the phytotoxicity of the end product (substrate) even when used immediately (Fig. 2C-D).

The twin-disc refiner is a large disc mill operating at high speed and pressure (+/- 4000 kilopascals = ~580 PSI) with internal temperatures reaching 220 – 400 °F (110 – 200 °C). This technique often has a water bath phase where wood chips are pre-soaked in a pressurized heated vessel for several minutes before being forced through the rotating discs. In this scenario, there is a solubilization and volatilization phase of the process which are effective at removing harmful wood extractives.

Lastly, the practice of co-refining wood chips with some percentage or peat, bark, or other material has been shown to be effective in further reducing (by dilution) wood phytotoxicity in the substrate material produced. Co-refining wood with other materials can be done with any of the three machine types mentioned above.

Substrate preconditioning

These methods are aimed at hammer-mill processed wood products as a result of the lack of sufficient heat/pressure generated in the mill.

Extruded or disc-refined commercial wood substrates have not been shown to need additional corrective measures to reduce toxins.

For hammer-milled wood substrates, aging has been shown to be the best and most effective method of reducing green wood toxins. Aging of wood can occur at different stages including the storage of harvested trees for a period of months prior to processing (Fig. 3A), aging of wood chips (under shelter preferred; Fig. 3B), aging of processed wood substrate outdoors or under shelter (Fig. 3C), or processed substrate aged in totes (Fig. 3D).

Aging, often called “seasoning”, of wood chips in piles for two weeks has been shown to be as effective in reducing toxins as aging whole logs for six months. The season of the year that aging occurs also will affect the duration needed to effectively mitigate the wood toxins due to temperature and rainfall fluctuations.

Aging of processed substrate in totes has received the most research over the past decade with the general recommendation that 4-6 weeks be allowed for the process. Longer periods of time do not negatively affect the quality of the end product.

However, aging large piles of fresh pine wood (sawdust or processed fiber) similar to pine bark substrates has not been perfected at this time and seems to be less consistent, more time consuming, and more variable than other forms of aging.

Preliminary research suggests that processed fresh pine wood substrates can also be dried at high temperatures very quickly to reduce (volatilize) harmful chemicals (Fig. 4A), although the exact temperature and duration needed are not yet fully understood.

Industrial dryers/drying can add an additional cost to the substrates, but based on how cheap hammer milled substrates can be produced, this added expense still makes this a viable economic option.

Other practices that have been explored with varying levels of effectiveness include the addition of charcoal, brown coal/lignite, or pulverized biochar products to wood substrates to bind the toxins, preventing them from affecting plant growth (Fig. 4B). Substrate steaming (pasteurization) in soil carts (Fig. 4C) and substrate washing or soaking in cold and hot water have also been investigated but the results are varied and inconsistent.

Additional strategies explored in reducing wood toxicity include the inclusion of peat, bark, or coconut coir (non-toxic substrate materials) to wood, thus reducing the wood percentage in the final substrate (Fig. 5A). This has been the most practiced strategy over the past decade since hammer milled pine substrates were first investigated (2004 – 2008) to be used at 100%. Since then, the most common wood product inclusion rate has been 20–40%, thus reducing the threat of green wood toxins. Research continues on this topic and is needed before more hammer milled wood products are used reliably and consistently.

Production practices

If fresh hammer milled wood materials (or pine sawdust, though not recommended at this time) are used in substrates without any preconditioning, there are practices that could help reduce plant stunting and other growth defects.

The most proven effective way to reduce wood toxins in containers is to leach them with water. Leaching containers with clear water frequently for a week (or as often as possible without imposing more detriment to the plants) has been shown to be effective in removing the toxins from the container (Fig. 4D).

Leaching of substrate-filled containers with over-head irrigation prior to planting has also been successful for some growers. Experiments have been conducted on various container sizes, leaching frequencies, drainage rates, and limited or stratified wood layers and volumes (Fig. 5C) to better understand how to solve production problems with wood substrates if they occur. Secondary to leaching, doses of high fertility have in some cases been shown to overcome phytotoxicity of young herbaceous crops including germinated seedlings (Fig. 5B).

However, there are conflicting reports as to the role that fertilizer can possibly play in mitigating toxins, as it may be the leaching of the applied fertigation that is actually reducing the toxins. A combination of leaching and increased fertility can mitigate any negative growth, allowing for healthy plants to be produced in substrates with very high wood percentages (Fig. 5D).

As we continue to learn more about practical and cost-effective methods of reliably removing toxins from fresh hammer milled wood, as well as some sawdust and other wood industry by-products, it is likely that these cheap materials will be used more frequently as substrate components. As a result, these developments will drive the increased production of these cheaper wood products across the US (and in parts of Europe) which should keep costs low as a result of limited transportation distance and manufacturer/supplier competition.

And in the meantime, it should be noted that there are several commercial wood fiber products on the market that are toxin-free and available for immediate use.

The author is an Associate Professor and Director of the Horticultural Substrates Laboratory at NC State University. Jackson can be reached at Brian_Jackson@ncsu.edu.

Photo courtesy of Lauryn Polito

Through career exploration, work experience and input from friends and family, Lauryn Polito now knows exactly what she wants to do with her life — own and operate her own greenhouse.

Polito, 19, is currently pursuing a degree in horticulture, with a concentration in floriculture and ornamentals, at Mississippi State University. But before college, Polito hadn’t yet realized her dream of being a small business owner.

“At the beginning of high school, I thought I wanted to be a physical therapist,” she says. “But after shadowing someone, I realized it wasn’t what I wanted to do. My mom looked at me one day and said, ‘Lauryn, why don’t you do something with plants?’ Because our back porch is covered with house plants.”

Polito took her mother’s words to heart and knew that it was the right choice for her.

“Going into college, my major was in environmental science and agricultural systems because I knew I wanted to do something involving plants but didn’t really know what I wanted to do,” she says. “After talking to my advisor and telling him I wanted to start my own business one day… he told me to look into horticulture. I thought it’d be the best major for what I want to pursue in life.”

The Trussville, Alabama, native says her classes have given her an even greater appreciation for greenhouses.

“I’ve enjoyed learning about the inner workings of greenhouse management. I actually didn’t know how big greenhouses could be, especially at commercial scale. Gaining that knowledge on the stuff I’m passionate about is great,” she says. “Living in a suburb, there are a lot of greenhouses and plant shops around us and they make me so happy. When I go in there, I could spend hours in there. I can just see myself doing that one day and being happy.”

Polito says that she’d love to incorporate a wedding venue into her future greenhouse so she can do floral arrangements as well.

“I’ve worked at a wedding venue for five years now and it’s one of my favorite things about coming back home from college,” she says. “In my experience there, I’ve gotten to work with a lot of florists and that was another way horticulture interested me.”

Polito adds she loves being around people and being outside, so she also took the time last summer to volunteer at the Birmingham Botanical Gardens as a camp counselor.

“That was really fun,” she says. “It was a week-long thing and I got a group of kindergartners. We’d go on nature walks, and seeing little kids passionate about nature and loving where they were was really cool.”

Before she sets out to start her own business one day, Polito says she’d like to get a research job first in hopes to help end world hunger.

“I’m very passionate about world hunger and have been since high school,” she says. “I want to work with a large organization to help end world hunger and find the best methods to grow sustainable products for vast numbers of people.”